When passing a single argument to an aggregate function, that argument can be preceded by the keyword DISTINCT, which filters out duplicate values.
For all aggregations other than COUNT( * ), NULL and missing values are ignored.
Function 
SQLite 
Description 

AVG( num_expr ) 

Computes the average of num_expr for the rows in the group. Num_expr must be numeric. 
COUNT( expr ) COUNT( * ) 

Counts the number of times expr is not NULL in the group. COUNT( * ) returns the total number of rows in the group. 
GROUP_CONCAT( expr, <separator = ’,’> ) 
Yes 
Concatenates all nonNULL values of expr and returns them as a string. Numeric values of expr are converted to character. If separator is present, it is placed between the values. The default separator is a comma. DISTINCT can be used only with GROUP_CONCAT() if separator is not specified. 
MAX( expr ) 

Returns the maximum value of expr in the group. Expr can be character or numeric. 
MIN( expr ) 

Returns the minimum value of expr in the group. Expr can be character or numeric. 
STDDEV_POP( num_expr ) 

Computes the population standard deviation of num_expr for the group. 
STDDEV_SAMP( num_expr ) 

Computes the sample standard deviation of all num_expr for the group. 
SUM( num_expr ) 

Returns the sum of num_expr for the group. If no nonNULL values are found, SUM() returns NULL. 
TOTAL( num_expr ) 
Yes 
Same as SUM( num_expr ), except TOTAL() returns 0.0 if no nonNULL values are found. 
VAR_POP( num_expr ) 

Computes the population variance of num_expr for the group. 
VAR_SAMP( num_expr ) 

Computes the sample variance of num_expr for the group. 